Vehicles may include cooling systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the hot engine, and the heated coolant is then circulated through a radiator near the front of the vehicle. Heated coolant may also be circulated through a heat exchanger to heat a passenger compartment. The cooling system may include various components such as various valves and one or more thermostats.
As such, the various cooling system components may need to be periodically diagnosed. In some engine cooling systems, an opening of the various valves may be adjusted to thereby maintain different coolant temperatures in different regions of the coolant line. For example, the coolant temperature near an engine block can be maintained different from a coolant temperature near a thermostat, at least temporarily. The temperature differential may provide fuel economy and performance advantages during selected engine operating conditions. The inventors have recognized that in such cooling systems, if even one of the cooling system valves is degraded, it may not be clear whether an increase in coolant temperature in a region of the cooling system is due to the explicit change in valve positions or due to an unexpected overheating of an engine system component.
In one example, some of the above issues may be addressed by a method comprising, during an engine cold start, individually closing and opening each of a plurality of cooling system valves to stagnate a volume of coolant in a section of the cooling system while exposing a cooling system thermostat to a remaining volume of coolant; and diagnosing each of the plurality of valves based on a change in the coolant temperature sensed at the thermostat during the individual closing and opening. In this way, cooling system valve degradation may be determined based on various thermal differentials created in different regions of the cooling system.
For example, a cooling system may be configured to circulate coolant to various vehicle system components via a plurality of valves (including a bypass shut-off valve, a heater shut-off valve, a thermostat valve, a transmission cooling valve, a transmission heating valve, etc.). During an engine cold start, a heater shut-off valve may be closed for a first duration to stagnate coolant at the engine and expedite engine warm-up. Then, after the first duration, the heater shut-off valve may be opened to circulate the coolant at the cooling system thermostat following passage through a heater core. A coolant temperature may be monitored while the valve is closed and then after the valve is opened. As such, based on cabin heating demands, the coolant temperature post heater core may vary, and accordingly a coolant warm-up profile may vary. For example, after the valve is opened, a volume of relatively cooler coolant may be released into circulation, leading to a sudden drop in engine coolant temperature. Based on a change in coolant temperature sensed at the thermostat during the closing and opening of the heater shut-off valve, the heater shut-off valve's degradation may be determined. Specifically, the drop in coolant temperature may indicate that the heater shut-off valve is functional.
Likewise, following diagnosis of the heater shut-off valve, a bypass valve may be opened and closed and a change in coolant temperature over the closing and opening of the valve may be used to identify bypass shut-off valve degradation. Similar approaches may be used to identify degradation in transmission cooling or heating valves, as well as the functionality of a grill shutter system of the cooling system. In this way, by diagnosing each and every component of the cooling system, changes in coolant temperature resulting from valve degradation may be better distinguished from those caused by engine overheating. In addition, a variable and controllable coolant temperature may be achieved using the existing set of cooling system valves.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.